mathematics
posted by joshua .
1. If $ is defined for all positive numbers x and y by x$y = 3x + 8y  y^3, then 10$2 =
A. 38
B. 102
C. 14
D. 20
2. If & is defined for all positive numbers w and z by w & z = 15wz  10w + 2 then 3 & 4 =
A. 67
B. 77
C. 142
D. 152
3. All of the following are in the domain of f(x) = 5/ x + 2 except:
A. 5
B. 5
C. 2
D. 2
could you explain to me how to get the answer for them

1 and 2
the operations are defined, so just sub in as defined.
1.
10$2 = 3(10) + 8(2)  2^3 = ....
same for #2
3. f(x) = 5/x + 2
the function is defined for all real values of x, except x = 0
This is not one of your choices, so the question is bogus.
If you meant f(x) = 5/(x+2) , then the function is defined for all real values of x, except x = 2